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/* Chrysalide - Outil d'analyse de fichiers binaires
* shuffle.c - permtutation aléatoire des éléments d'un ensemble fini
*
* Copyright (C) 2016-2017 Cyrille Bagard
*
* This file is part of Chrysalide.
*
* Chrysalide is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 3 of the License, or
* (at your option) any later version.
*
* Chrysalide is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with Chrysalide. If not, see <http://www.gnu.org/licenses/>.
*/
#include "shuffle.h"
#include <malloc.h>
#include <stdlib.h>
#include <string.h>
/******************************************************************************
* *
* Paramètres : panel = instance d'objet GLib à traiter. *
* *
* Description : Mélange le contenu d'une liste. *
* *
* Retour : - *
* *
* Remarques : - *
* *
******************************************************************************/
void shuffle(void *base, size_t nmemb, size_t size)
{
char *list; /* Conversion pour le confort */
char *tmp; /* Lieu de transition */
size_t i; /* Boucle de parcours */
size_t j; /* Emplacement aléatoire */
/**
* Application de l'algorithme Fisher-Yates.
*
* Cf. https://en.wikipedia.org/wiki/Fisher%E2%80%93Yates_shuffle
*
* En version hors-ligne, cela donne :
*
* -- To shuffle an array a of n elements (indices 0..n-1):
* for i from 0 to n−2 do
* j ← random integer such that i ≤ j < n
* exchange a[i] and a[j]
*
*/
if (nmemb > 1)
{
list = (char *)base;
tmp = malloc(size);
for (i = 0; i < (nmemb - 1); i++)
{
j = i + rand() % (nmemb - i);
if (j != i)
{
memcpy(tmp, list + i * size, size);
memcpy(list + i * size, list + j * size, size);
memcpy(list + j * size, tmp, size);
}
}
free(tmp);
}
}
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